1. Field of the Invention
The present invention relates to an image forming apparatus that forms a latent image on a latent image carrier by performing pixel division modulation on an input image signal, driving a laser light source based on the pixel-division-modulated image signal to modulate a laser beam emitted from the laser light source, and scanning the latent image carrier using the modulated laser beam, and a main scanning scale correcting method for such an image forming apparatus.
2. Description of the Related Art
In general, an image forming apparatus such as a laser beam printer or a digital copier is configured to form a latent image by using a laser beam driving circuit to drive a semiconductor laser using an image signal to modulate a laser beam emitted by the semiconductor laser, and raster-scanning the modulated laser beam over on a photosensitive drum using a rotary polygon mirror.
In an apparatus of this type having a plurality of semiconductor lasers, the scale of the latent image varies depending on a position on the photosensitive drum which is irradiated with a laser beam from each of the semiconductor lasers. Further, the rotary polygon mirror has finish accuracies between the surfaces thereof. Accordingly, a position at which a latent image starts to be drawn varies depending on the surface. Furthermore, with an image forming apparatus that can print on both surfaces of a sheet, the size of the sheet decreases after fixation, and consequently the size of a printed image on one surface of the sheet differs from that of an image on the other surface even if the proportion of the latent image on one surface is the same as that of the latent image on the other surface.
To solve this problem, a method has been proposed in which the size of a printed image is corrected by applying, at a desired point, an image clock used to transfer image data to control the length between adjacent image data (for example, Japanese Laid-Open Patent Publication (Kokai) No. 2000-238342).
However, in the above conventional method, the image clock is corrected, and the image data to be interpolated is fixed. Consequently, blank spaces may be created in those portions of the data in which the image clock is slightly elongated. Therefore, printing quality may be degraded.
It is a first object of the present invention to provide an image forming apparatus that is capable of securing required printing quality by properly correcting a main scanning scale, and a main scanning scale correcting method for such an image forming apparatus.
It is a second object of the present invention to provide an image forming apparatus that is capable of securing required printing quality by properly correcting a printing proportion, and a main scanning scale correcting method for such an image forming apparatus.
To attain the first object, in a first aspect of the present invention, there is provided an image forming apparatus comprising a pixel division modulating device that performs pixel-division modulation on an input image signal and outputs the pixel-division-modulated image signal in synchronism with an image clock of a fixed frequency, a laser light source, a driving device that drives the laser light source based on the image signal outputted from the pixel division modulating device to modulate laser light emitted from the laser light source, a latent image carrier, and a scanning device that scans the latent image carrier using the laser light emitted from the laser light source to form a latent image on the latent image carrier, the pixel division modulating device comprises a correction device that, for each of at least one correction point on one of lines along which scanning is carried out on the latent image carrier by laser light, adds final bit data of pixel-division-modulated pixel data of a pixel preceding the correction point to pixel-division-modulated pixel data of a pixel located at the correction point as leading bit data thereof, and sequentially shifts predetermined bit data of pixel-division-modulated pixel data of each of pixels subsequent to the correction point to a next pixel to generate pixel data of at least one new pixel added for the one line, and an output device that outputs the pixel data of the generated at least one new pixel in synchronism with the image clock of the fixed frequency.
To attain the first object, in a second aspect of the present invention, there is provided an image forming apparatus comprising a pixel division modulating device that performs pixel-division modulation on an input image signal and outputs the pixel-division-modulated image signal in synchronism with an image clock of a fixed frequency, a laser light source, a driving device that drives the laser light source based on the image signal outputted from the pixel division modulating device to modulate laser light emitted from the laser light source; a latent image carrier, and a scanning device that scans the latent image carrier using the laser light emitted from the laser light source to form a latent image on the latent image carrier, the pixel division modulating device comprises a correction device that, for each of at least one correction point on one of lines along which scanning is carried out on the latent image carrier by laser light, adds leading bit data of pixel-division-modulated pixel data of a pixel preceding the correction point to pixel-division-modulated pixel data of a pixel located at the correction point as leading bit data thereof, and sequentially shifts predetermined bit data of pixel-division-modulated pixel data of each of pixels subsequent to the correction point to a next pixel to generate pixel data of at least one new pixel added for the one line, and an output device that outputs the pixel data of the generated at least one new pixel in synchronism with the image clock of the fixed frequency.
To attain the first object, in a third aspect of the present invention, there is provided a main scanning scale correcting method for an image forming apparatus comprising a pixel division modulating device that performs pixel-division modulation on an input image signal and outputs the pixel-division-modulated image signal in synchronism with an image clock of a fixed frequency, a laser light source, a driving device that drives the laser light source based on the image signal outputted from the pixel division modulating device to modulate laser light emitted from the laser light source, a latent image carrier, and a scanning device that scans the latent image carrier using the laser light emitted from the laser light source to form a latent image on the latent image carrier, the method comprising the steps of adding, for each of at least one correction point on one of lines along which scanning is carried out on the latent image carrier by laser light, final bit data of pixel-division-modulated pixel data of a pixel preceding the correction point to pixel-division-modulated pixel data of a pixel located at the correction point as leading bit data thereof, and sequentially shifting predetermined bit data of pixel-division-modulated pixel data of each of pixels subsequent to the correction point to a next pixel to generate pixel data of at least one new pixel added for the one line, and outputting the pixel data of the generated at least one new pixel in synchronism with the image clock of the fixed frequency.
To attain the first object, in a fourth aspect of the present invention, there is provided a main scanning scale correcting method for an image forming apparatus comprising a pixel division modulating device that performs pixel-division modulation on an input image signal and outputs the pixel-division-modulated image signal in synchronism with an image clock of a fixed frequency, a laser light source, a driving device that drives the laser light source based on the image signal outputted from the pixel division modulating device to modulate laser light emitted from the laser light source, a latent image carrier, and a scanning device that scans the latent image carrier using the laser light emitted from the laser light source to form a latent image on the latent image carrier, the method comprising the steps of adding, for each of at least one correction point on one of lines along which scanning is carried out on the latent image carrier by laser light, leading bit data of pixel-division-modulated pixel data of a pixel preceding the correction point to pixel-division-modulated pixel data of a pixel located at the correction point as leading bit data thereof, and sequentially shifting predetermined bit data of pixel-division-modulated pixel data of each of pixels subsequent to the correction point to a next pixel to generate pixel data of at least one new pixel added for the one line and outputting the pixel data of the generated at least one new pixel in synchronism with the image clock of the fixed frequency.
Preferably, in the first to fourth aspects, the at least one correction point are determined in advance.
Also preferably, in the first to fourth aspects, the number of the at least one correction point is determined to be an integral multiple of resolution of pixel division modulation executed by the pixel division modulating device.
Also preferably, in the first and second aspects, the image forming apparatus further comprises an image write reference signal output device that outputs an image write reference signal, and a delay device that delays timing in which output of the pixel data is started in synchronism with the image clock of the fixed frequency, by a predetermined time period for each of preset lines in response to the image write reference signal.
Also preferably, in the third and fourth aspects, the image forming apparatus further comprises an image write reference signal output device that outputs an image write reference signal, and the method further comprises a step of delaying timing in which output of the pixel data is started in synchronism with the image clock of the fixed frequency, by a predetermined time period for each of preset lines in response to the image write reference signal.
To attain the second object, in a fifth aspect of the present invention, there is provided an image forming apparatus according to the first and second aspects which each further comprises an image write reference signal output device that outputs an image write reference signal, and a delay device that delays timing in which output of the pixel data is started in synchronism with the image clock of the fixed frequency, by a predetermined time period for each of preset lines in response to the image write reference signal.
To attain the second object, in a sixth aspect of the present invention, there is provided a main scanning scale correcting method according to the third and fourth aspects, wherein the image forming apparatus further comprises an image write reference signal output device that outputs an image write reference signal, and wherein the method further comprises a step of delaying timing in which output of the pixel data is started in synchronism with the image clock of the fixed frequency, by a predetermined time period for each of preset lines in response to the image write reference signal.
According to the first to fourth aspects of the present invention, it is possible to secure required printing quality by properly correcting the main scanning scale.
According to the fifth and sixth aspects of the present invention, it is possible to secure required printing quality by properly correcting the printing proportion.
The above and other objects, features, and advantages of the present invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings.